Noise generating circuit



March 13, 1962 P. H. PETERS, JR., ET AL 7 NOISE GENERATING CIRCUIT Filed Nov. 25, 1953 2. l6\ a 1 l9 m 20 1 l8 INVENTORS, PHIL/P h. PETERS JR, DONALD A. W/LBUR.

United States Patent 3,025,475 NGISE GENERATING CIRCUIT Philip H. Peters, Jr., Schenectady, and Donald A. Wilbur,

Albany, N.Y., assignors to the United States of America as represented by the Secretary of the Army Filed Nov. 23, 1953, Ser. No. 393,969 4 Claims. (Cl. 331-78) This invention relates to improvements in noise generating circuits and more particularly to a circuit utilizing a self-quenched magnetron.

It is an object of this invention to provide a circuit for simultaneously operating a magnetron in a plurality of modes, one the traveling wave mode and the other a negative resistance mode.

It is a further object of this invention to provide a magnetron operating in two modes which is self quenched at the frequency or frequencies of the lower frequency mode.

It is a further object of this invention to provide a new and improved noise generating circuit which is light in weight and simple, and inexpensive to construct.

In accordance with the invention, there is provided a magnetron energized to operate simultaneously in two modes, one of which is a high frequency traveling wave mode and the other of which is a relatively low frequency negative resistance mode. An output circuit having a high impedance at the frequency of the traveling wave mode is coupled to the magnetron. The frequency or frequencies in the negative resistance mode are determined by one or more circuits tuned to said frequency or frequencies coupled to the magnetron. So connected, there is built up across the circuit or circuits tuned to the negative resistance mode a voltage which quenches the magnetron at the frequency of the negative resistance mode.

The features of the invention which are believed to be novel are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and method of operation, together with further objects and advantages thereof, may best be understood by reference to the following description taken in conjunction with the accompanying drawing in which:

FIG. 1 is a schematic diagram of a preferred embodiment of the invention; and

FIGS. 2, 3 and 4 are schematic diagrams illustrating modifications of the circuit shown in FIG. 1.

Referring now to FIG. 1, there is shown a traveling wave magnetron 11 having a cathode 14 and a plurality of interleaving anode sections, all enclosed in an envelope 15. Alternate anode sections are connected to a first conductive ring 12 and the remaining anode sections to a second conductive ring "13. The cathode 14 is connected to the negative terminal of a source of potential 22, the positive terminal of which is grounded.

The output of the magnetron 11 is supplied to a tuned transmission line, comprising parallel wires 16 and 17, which are cut to the traveling wave frequency output of the magnetron. Connected between points A, A is a capacitor 19 which has a value such that it presents a low impedance at the traveling wave frequency and a high impedance at the frequency of the negative resistance mode. Resistor 18 represents a radio frequency load such as an antenna. It is slidable along lines 16 and 17 and is normally located at a point of proper impedance match. Connected to points A, A is a doubly tuned transformer 20, 21, the tuning of which determines the negative-resistance-mode frequency or frequencies. There may be substituted for circuit 20, 21 one of the tuned circuits shown in FIGS. 2, 3 or 4. The circuit shown in FIG- URE 2 comprises a plurality of double tuned transformers, each transformer being tuned to a different frequency in the range of the negative resistance mode of operation.

3,Z5, i?5 Patented Mar. 13, 1952 FIGURE 3 includes a plurality of series connected resonant tuning circuits each circuit adapted to be resonant at a discrete modulating frequency in the range of the negative resistance mode and comprising a pair of oppositely arranged inductance coils having their mutual end terminals interconnected by a capacitor. FIGURE 4 is similar to that of FIGURE 3 except that each of the resonant tuning circuits now comprises a pair of oppositely arranged capacitors having their mutual end terminals interconnected by an inductance coil. By using any of the three arrangements shown, multiple frequency self-quenching modulating circuits are provided to further increase the instability of the modulating circuit and thus effect a more efiicient jamming device.

As is well known in the art, the traveling wave mode of operation has a definite D.C. starting potential. Changes in this DC. potential affect both the traveling wave frequency and the radio frequency power output of the magnetron. The negative resistance mode is noncritical of DC. anode potential. Therefore, if the DC. potential applied to the magnetron is adjusted to provide the desired traveling wave frequency it will also he satisfactory for the negative resistance mode.

The magnetron has the negative resistance characteristic over a Wide frequency range extending from a very low frequency up to frequencies at which electron transit times modify the behavior. This upper limit may be in the megacycle region. The frequency or frequencies of operation in the negative resistance mode are determined by the tuning of the low frequency circuit connected across A, A.

The theory of operation of a traveling wave magnetron independently in the traveling wave mode is explained indetail in applicants copending application titled Magnetron and Systems Therefor, Serial No. 169,712, filed June 26, 1950, now Patent No. 2,774,039. Operation of a magnetron independently in the negative resistance mode is explained briefly on pages 67 and 68 of the volume Radar Systems and Components, by the Bell Laboratories Staff, published by D. Van Nostrand Co., Inc., in 1949.

In operation, the circuit shown in FIG. 1 is made to self-quench by the simultaneous operation of the magnetron in two modes. As can be seen, circuit 20, 21, which determines the negative resistance: frequency is effectively in series with the transmission line output circuits 16, 17 of the magnetron. Voltage periodically builds up across circuit 2t 21 at the negative resistance freqency and this voltage quenches the traveling wave mode of the magnetron at said frequency.

In a circuit actually built, a miniature type Z206l magnetron was operated in a traveling wave mode at 300 megacycles. The negative resistance or quench frequency could be adjusted to between one and four megacycles by adjustment of the frequency to which circuits 20, 21 were tuned. When self-quenched, the traveling wave mode circuit delivered an average output of about milliwatts compared with an output of about 200 milliwatts when not quenched. Self-quenching has the advantage that a certain amount of instability in the quench modulating rate occurs and this tends to increase the noisy character of the signal.

As mentioned previously, more than one doubly tuned transformer, each tuned to a different modulating frequency, may be used. This tends further to increase the instability in the modulating frequency.

The circuits described above generated a noise bandwidth of approximately 20 megacycles, 10 megacycles on each side of the 300 megacycle traveling wave frequency. With this noise, it was possible to obliterate a pulse received on a receiver having a four megacycle bandwidth.

Some important advantages of the noise generator described herein are that it is very simple, it may be batterypowered, it is light in weight, and may be self-contained.

While there has been described What is at present considered the preferred embodiment of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is aimed in the appended claims to cover all such changes and modifications within the true spirit and scope of the invention.

What is claimed is:

1. A noise generating circuit comprising a magnetron, means energizing said magnetron so as to cause operation thereof in a plurality of modes, one a relatively high frequency traveling wave mode and the others relatively low frequency negative resistance modes, an output circuit coupled to said magnetron, said circuit having a high impedance at the frequency of said traveling wave mode, and means for periodically quenching said magnetron comprising a plurality of circuits in series with said output circuit, each of said last-named circuits being tuned to and operating at a diiferent frequency in said negative resistance mode.

2. The noise generating circuit in accordance with claim 1 wherein said last-named circuits comprise a pinrality of double tuned transformers.

3. The noise generating circuit in accordance with claim 1 wherein said last-named circuits comprise a plurality' of serially connected resonant circuits each including a pair of oppositely arranged inductance coils, the mutual end terminals of each of said pair of opposing inductances being interconnected by capacitors.

4. The noise generating circuit in accordance with claim 1 wherein said last-named circuits comprise a plurality of serially connected resonant circuits each including a pair of oppositely arranged capacitors, the mu tual end terminals of each of said pair of opposing capacitors being interconnected by an inductance coil.

Gutton Feb. 14, 1939 Braden Aug. 13, 1940 

